In conventional hydraulic injection-molding machines, a limit switch or the like has been used to set various set values, including changing positions for the mold closing and opening speeds of a clamping unit (mold clamper), injection-speed changing positions, changing positions for the rotating speed of a screw during metering, the ejection forward and reverse positions of an ejector, etc. Therefore, the set values have suffered only minor setting errors. Recently has been developed, however, an injection-molding machine which uses servomotors as various drive sources, and is controlled by means of an NC unit. In the injection-molding machine of this type, the various set values are set in the form of numerical values through a keyboard of a manual data input unit with a CRT display (hereinafter referred to as MDI/CRT).
The control of the injection-molding machine by means of the NC unit is performed in accordance with the various set values indicative of, for example, the changing positions for the mold closing and opening speeds of the clamping unit, the changing positions for the injection speed of an injection unit, and the ejector forward and reverse positions of the ejector. In mold opening control of a mold, for example, the mold typically is first moved to an acceleration start position P1 at a mold release speed V1, as shown in FIG. 1. Then, the mold is moved from the acceleration start position P1 to a deceleration start position P2 at a high mold opening speed V2. From the deceleration start position P2 to a mold opening end position P3, the mold is moved at a low mold opening speed V3. Usually, an NC program for such mold opening control is composed of a macro-program for higher universality. For example, the velocities V1 to V3 and the positions P1 to P3 are set by using macro-variables #500 to #505 which can be set to various values. Thus, the following NC program is prepared.
Y#503 F#500 PA1 Y#504 F#501 PA1 Y#505 F#502
Here symbols Y and F designate a clamp axis and a speed, respectively. According to the program for mold opening control, composed of the above three blocks, a command for movement is delivered in the first block such that the mold is moved to the position P1, which is set by means of the macro-variable #503, at the speed V1, which is set by means of the macro-variable #500. When the first block terminates, a command is delivered in the second block such that the mold is moved to the deceleration start position P2, which is set by means of the macro-variable #504, at the speed V2, which is set by means of the macro-variable #501. In the third block, a command is delivered such that the mold is moved to the mold opening end position P3, which is set by means of the macro-variable #505, at the speed V3, which is set by means of the macro-variable #502. The mold opening operation is controlled in this manner.
Unless there are relations:
clamp stroke .gtoreq.#505 .gtoreq.#504 .gtoreq.#503 .gtoreq.0 between the set values based on the macro-variables #503, #504 and #505, the clamping unit suffers an abnormal mold opening operation such that the mold closes again after being opened, for example, even during a mold opening cycle in which the mold should be driven only in the opening direction.
In order to accomplish required operations in various control modes (items) of the injection-molding machine, as well as the aforementioned mold opening operation, there must be predetermined relations, as mentioned later in detail, between the set values related to the operations concerned. If these requirements are not fulfilled by the inputted set values, the control operations suffer troubles and are performed wrongly, as described above in connection with the mold opening operation.